1. Field of the Invention
This invention relates to the field of security systems for monitoring restricted areas, such as in and around a vehicle, and provides more features, greater range of operator-system interface, and more user-friendly operation than those systems in the prior art. More particularly, this invention provides for remote communication from a remote-control transmitter to an alarm controller using a code word having interlaced/scrambled fixed bits and hopping/changing bits. This provides for additional security because a potential intruder is unable to decode/descramble the security code as the information therein is unpredictably and constantly changing from transmission to transmission and from transmitter to transmitter.
2. Description of Prior Art
At the present time there are a number of security systems available in the market. Many of these security systems employ remote-control transmitters to communicate commands to the associated system alarm controllers. A number of these systems use fixed code transmissions. In conventional fixed code transmissions, all non-channel identification bits remain the same from transmission to transmission when transmitted from the same transmitter. A typical transmission includes a synchronization bit or a preamble which is a group of bits used to wake the receiver up and preset its automatic gain control (AGC). This is followed by the remote control transmitter's serial number, address and/or channel identification bits. There can be as few as eight bits and as many as several hundred. Within this bit stream are the transmitter channel identification bits, anti-scan bits and other miscellaneous bits. These miscellaneous bits are employed for anti-scan purposes and/or to make the code word longer to hide the real address code more effectively.
There are two important security shortcomings to the fixed transmission techniques of the prior art. The transmitted codes are usually fixed or the number of code combinations is relatively small. These shortcomings lead to unauthorized access to a protected area. Such unauthorized access may be obtained by scanning through all of the combinations on systems having limited code combinations. Additionally, an intruder with a code grabber can record a conventional fixed code transmission of practically any length if its frequency is known is known to him or her. An intruder can use this recorded information to re-transmit the code at a later time and gain access to the area protected by the security system. Moreover, frequencies allotted to security systems are fixed in several countries of the world, which makes it easy to make and use a code grabber. The code grabbing principle is widely recognized as a very serious threat in these areas where the use of multiple radio frequencies is not permitted. Code grabbing remains a serious threat to all current conventional fixed code radio frequency remote-control security systems.
To improve security, code hopping may be utilized to prevent code capturing and scanning. The same is described in the U.S. Pat. No. 5,103,221, issued on Apr. 7, 1992, to Serafino Memmola. In code hopping systems a different or changing code word is used with every transmission. Most conventional code hopping systems are designed with fixed codes and hopping codes separated into their two respective sections. Other security systems only employ hopping words thereby changing the entire code of the word with each transmission. This makes it easy for an intruder to analyze and calculate simple hopping code algorithms used to change the hopping portion of the code word because the fixed and the changing bits are known to him. To overcome the shortcomings, these systems require more complex, longer word length and/or more sophisticated hopping algorithms to accomplish the same result as a less complex scrambled code hopping system of the present invention.
Scrambled code hopping is a method which provides high security, remote, radio frequency transmission of information or commands between a wireless, remote-control transmitter and a receiver of an alarm system. This technology is useful in remote-controlled vehicle alarms, automatic garage doors and other systems which rely on wireless communications. This invention provides for means to complicate the descrambling or deciphering of the transmitted code by scrambling or interlacing the fixed and hopping bits of the data word transmitted from a remote-control transmitter to an alarm controller. Scrambling the fixed and hopping codes provides for extreme complexity in descrambling the position, value and the significance of each transmitted bit, thereby establishing an effective barrier against intruders. In a scrambled transmission device of the present invention, it could take hours for a given hopping bit to change during extended transmission periods, thereby making it difficult to identify which bits are hopping and which bits are fixed. It also makes it difficult or impractical to decipher the security code. In addition, the present invention requires less complicated and simpler code hopping algorithms to achieve a high level of security at a reasonable cost.